Fish environmental guilds as a tool for assessment of ecological condition of rivers

The form, hydrology and functioning of rivers worldwide have been increasingly modified by a range of human activities. The impacts of these changes on the fish faunas of rivers need to be assessed for biodiversity conservation and fisheries management. Reliable and cost effective indicators of fish assemblage responses to hydrological, morphological and functional changes in a river are required. Given the large number of fish species present in many rivers, reliance on a single indicator species is problematic. The present paper proposes the use of environmental guilds for this purpose. Building on prior studies, we propose a series of environmental guilds based on common patterns of response by fish species to changes in river flow and geomorphology. A general framework consisting of two upland stream guilds, three lowland lentic guilds, four lowland lotic guilds, two generalist guilds and five estuarine guilds is proposed. Considering the large numbers of species present in many river and estuarine systems and the flexibility of their behaviour, many species will be difficult to classify. Further development of the proposed guild classification at the level of individual basins is anticipated, particularly in river systems with highly variable hydrology and many opportunistic species. Nevertheless, this general scheme would be easily and rapidly applied to a wide variety of local circumstance, as well as to the description of the general trends in fish population and assemblage structure Occurring during river development. Copyright (c) 2006 John Wiley & Sons, Ltd.